Over at my official website, I have posted about what to do if you have a DUI arrest on your record and you plan to enter (or even stop over) in Canada. Yes, I said arrest, not conviction.
Short version: be prepared, by obtaining official court documentation of your case, and try to get your Canadian “seal of approval” in advance.
The good news is that Canada is getting less restrictive, but it is still a major hassle.
Here is the link to the story: http://www.illinoisduilawyer.com/il-dui-lawyer/oh-canada-entering-canada-with-a-dui-on-your-background